Egbert von lepel



Jan. 18, 1927, E. VON LEPEL CURRENT com/Enma E QR mngTIou sYs'x-i Filed March- 25, 1925 Patented Jan. 1 8, 1927.

- UNITED STATES 1 4.1,614,906 PATaN-rfoFFice.

EGBEItT VON LEPEL, QF BERLIN-CHARLOTTENBURG, GERMANY.

CURRENT CONVERTER roR IGNITION svsTnMs. i

Application led March 25, 1925i, Serial No'. 18,5853,4 landim Germany Auguri: 18, 1924. f

All, 'electric ignitin-g| devices hitherto known in connection with internal combustion engines did not result in full' satisfaction as interruptions in the working ofthe.

sparking plug occurred in spite ofthe provlsion of condesers and spark-gaps. `Also the connection of the sparking plug in series lof the ignition ,Jcurrent, upon 'deposits of soot or condensed particles present on the insulator or between the electrodes of the plug, converting the respective deposit into carbon, and incrusting this 'into the surface of the insulator. While the loose-particles of soot and the said condensed particles disappear, as a rule, spontaneously at full load theengine, the incrusted particles adhere firmly and form constant conducting bridge-a fora certain part of the current, in conse- -.quence whereof these bridges increase grad? 'ually so that the operation of lthe spark plug gets finallycompletely prevented. On this discovery mv present invention is based. l

My invention is illustrated diagrammati- -cally and hy'way of example in the accom'- panying drawings in which Figure 1 reveals the principle on which the" inventionv is based; Figure 2 is anotherdiagram also dealt with in the specification; Figures 3 and 4 show a section and an elevation of a high-'frequency current-converter for carr ving my inventioninto effect in a particularly economical way; and Figure 5 is also a-wiring diagram into which this converter is 1nserted.\

As is known, the failure `of ignition in errp'losion motrs is due very frequently to the fact that deposits of soot, oil, or dampness, whichset up a shunt to the spark gap, are formedon the surfaceof the spark plug insulation or between the poles of .the spark gap in; the spark plug. If the ohmicl resistance of such shunt circuits is great in com- .paris'on lto the resistance .which the spark gapfofgzthe ,sparkv plugpresents, then only very* -little 4currentvill flow through the lshunt. But if thersistance of the shunt gradually becomes less, then the percentage, of the whole available current, which passes y the through the shunt adually increases. With a vcertain value o ohmic resistance of the shunt circuit, there will then pass through the. shunt circuit a percentage of the whole `available current which is so great that the difference in potential which is necessary fortle formation of the Spark cannot be availa e. u

It was rst determined that the portion of the current which 'flowsthrough the shunt has the effect of reducing the ohmic resistance of the shunt. -This effect is to be exf plained by the intense heating resulting from the current, ofthe thin layer which forms the shunt. The ohmic resistance of a thin conducting layer which is present in the circuit in shuntV with the spark gap of the spark plug is decreased very much in the course of time by the ignition current itself, so that portion of the current which Hows through the shunt increases` constantly.

It was furthermore determinedl as a .basis for the present invention that the duration of each ignition current impulse in the case of the ignitionl devices in use up to now is comparativelywlong. The reason therefore is the following: In' the case of the usual high. tension ignition devices-whether they are formed as ignition coils withrfbattery ignition yo'r as magnets-the current is ros duced by the electromagnetic field of an lron` core. vThe secondary winding on the iron core has ,a very high self-inductioi, in order I that the high tension` mayY be produced which is necessary to break through the orig- .inal resistance of the spark gap of thel plug.

As soonl as the spark is formedthe original high resistance of the spark gap falls immediately'to a comparatively small value. A

luminous arc is thereby formed lwhich with -,respect to the secondary winding of the coil functions Qsir'ilarly toa -short circuit. The magnetic field in the iron is maintained -for a very llong time by the practicallysflort-circuited coil, sothat it can give up its energy only'very slowly and in the form of along continued weak current. Consequently' the time during which the ignition current flows is much .-longer than is expedient for ignition.

According to my discovery it is useful in case of the vplugsV being deiiled by sootV or th'e like, to have the necessary. electric tension of the plugs rising as steeply :1s-possible and to have it act as short aspossible upon Athe sootedplug. Y

The .v simplest-[way off performing this -v i could consist in storing the whole electric energy of each ignition-period in a suiicientl largecondensenand to discharge the store -up ener in one short and strong spark through t e spark-plug by means of inserting one of the well-knowntypes of quenching-gaps like those'used in wireless transmission. s

This way, however, proves to be unsuit able for the reason, that the necessarily varying number of: revolutions of the motor is not allowing the use of a sufliciently large condenser as the electric energy is far from being constant but using a smaller condenser even with a quenching gap of the best type known it is impossible to prevent the lowfrequency component existing after the high-frequency `discharge from. passing through the spark-plug, as the time required by the usual type; of quenching-gaps for their de-ionization is'much too long for the purpose. t

I therefore aimed at an arrangement allowing to fully interrupt `the current at a rate of some hundred thousand times in a second, so obviating the necessity of having a storing condenserof appreciable capacity.

The new means to fully interrupt the ignition-current at a rate of several hundred thousand times per second are the following:

Instead of a quenching spark-gap a storing-up gap is used, which consists `of a series of electrodes the spark-gaps between the .latter being not wider than from some thousandths to a few hundredths of a millimeter, whereasv the spark-gaps of the usual quenching-gaps amount to at least between one and two tenths of a millimeter.

Using a series of gaps of theI very short type indicated, the self-capacity of the source of high-tension combined with the self-"capacity of the circuit wires, which amount together to from 20 to l() cm., is

sufficient to act as storing-up capacity; the

'shape of the potential-curve resulting fromV inserting such series of very short gaps into the leads lto the spark-plug'is diagrammatically shown in Fig. 1;

In this figure the dotted line l represents the tension produced by the high-tension source its terminals beingv open.- The curves 2 represent the tension as it acts upon the spark-plug. From this diagram itis to beseen, that the potential necessary to break down the gap of the plug rises very steeply on the plug to the value 3, a damped highfrequency oscillation of a frequency of about som'e millions per second taking place at the first discharge and dying out before the second discharge of the same ignition-period begins, Vand so strong and short high-frequency impulses will occur a-great number of times during each ignition period, com- -busting the deposits bn the plug instead of incrusting them. Besides thereof, by the electrostatic action of these impulses the electrodes and thfeJ insulator of the spark-plug get consantly and very effectively cleaned,

because" he loose deposits' of soot or moisture are thrown off with considerable power.

In the intervals between these impulses the plug isgfull kept free of tension, this latter rising up slbwly on the storing gap, chargl ing meantimes the said small self-capacity.

The new process is' therefore based thereon, that the currentof long duration which normally flows through the spark plug is suppressed, in that 'an arrangement is combined /with thehigh tension circuit, which interrupts the current flow each time immediately after it originates and again restores it immediately after the interruption.. Through this alternate breaking of and restoring the current How, the current is split up into a series of short impulses rapidly following each other. Any current intervrupter acting sufficiently. quickly can, in

principle, be used for thispurpose.

The apparatus for converting the primarily low-frequency current into highfrequency current-impulses and consisting merely of a series of about 4t to 8 small electrodes with /the said very small gaps, will in the following be called the high-frequency current-converter. V

F or the sake of completeness the diagram figure represents the curve .of tension 2a at til) the plug, when no gap is used in series with the plug. As is to be seen from this diagram, the potential at the plugiis slowly increased to the breakdown-voltage 3 of the pluggap. Thereafter a short oscillatory Hush of current takes place diminishing the resistance of the gap so much that -a continuous' electric arc is maintained until the ignition-period is finished. l

During all this time the plug remains under tension'and more or less strong components of the current are flowing through the soot, carbonizing and incrusting it/into the insulator.

On comparing Figs. 1 and 2 it is apparent that thewhole time of the discharge process is shortened. The shortening, in fact, is very much greater than appears in the drawings, for with breaks and makesof the current circuit ensuing with suticient rapidity, the 4'whole time of discharge can be reduced to lessl than a tenth part of the normal time.k

The new process presents itself therefore as a very lmportant concentrating of energy, and

effects, accordingly, a likewise important in- 5 5; start with by means of a thin layer of paper Cil frequency current-converter it is very important to choose-the most suited material for the electrodes. The usual materials, viz, copper, brass or nickel, are very bad for'this purpose.

Except some expensive precious metals, as

vfor instance `w0lfram, those other metals are yespeciallysui-ted, the fusing orI combustion point'of whichis lbelow or very near their temperatures of incandescencc'. Metals ot' this kind areffor instance, aluminium, tin,

magnesium and high-grade alloys thereof; The use of these metals, etc., for series spaikgaps has been hitherto entirely unknown in the art of motoi" ignition.

Itis advisable to s elect metals, the residues of combustion of which or the loxides 'of which are nonconductive, as is the case especial'ly with aluminium, magnesium, and their alloys.

lVhen using electrodes of these materials no great parallel sparking surfaces are re-v qulred'as is the case with .the known quenching-ga s. The electrodes may be ball'- shap oreven pointed. No cooling-provisions are further needed.

It is suilicient to arrange the right num.-`

her of electrodes with a lQose microphonelike contact to one another and tohave by 'the discharge itself the. surfaces burned or oxidized. Thereafter the residues of combustion or the oxide, themselves, serve to keep the electrodes in the ri ht veryv short distance apartfr'om one anot er.`

It has been proved very practical to devise the high-frequency current-converter in the V shape of a small cable-socket as shown in Figs. 3 and 4, or to insert it into the body l of the plug itselfas it requires very little' space. l

In Figure 3 a section 'through al socket- 'shaped converter is shown. 10 represents a small insulating tube which contains the electrodes 11, 12, 13; these electrodes forming, for instance, seven gaps ofthe saidvery' short length. The end-electrode 11 is provided lin the example shown with a hole and a screw l14 for iixing it on the high-tension '-pole of the plug, and the otherend-electrode 13 has a smallerhole 15 to take upl the lead wire. The details of the converter may, of course,.be modified.

;It is furthermore practical to separatev from one another the fresh electrodes to or lacquer, these substances 'burning slowly away in the course of using theapparatiis and being no 'longer needed, when the said self-insulating layer ofoxide has formed.

placed eachsin l v Of course, as wel 'a single converter Fig. '5 shows how the converters may-be inserted in the' leads. The converters' 16 are series with one spark-plug 17 \might be placed betw en the source of voltage 18 and the distribuer 19,

. gets considerably weakened,

.The number of electrodes to 'be used 'de-l i pends on the voltage and on the output of energy of the source of tension.

Using, for instance, seven ga s the whole l drop of tension between the en s'of .the converter for getting the described eifect need not and should not exceed the amount or potential dro produced by a single ordinary gap of a out from 0,5 to 1,5 mm.

The great difference between the present converter and the well-known quenching gaps consists in the following features:

could beproduced under normal conditions amounts to about 300 volts even ifthe gap should be- 'the .smallest aimginavble. In-

'Thelowest voltage" bywhich ga .spark creasing. the widthof tliegap the 4drop of the potential on the gap increases in this way, thatto the initial voltage-drop is added the drop caused by the air-space. While the initial drop is practically constant, the )drop on the air-gap isextremely variable under the action of the. current passingl through that gap; the initial drop shall in the following becalled the cathode fall.

In my converter-having. those very short gaps I chiefly make useof the constant cathode fallf-obvating as much as possible.

the influence -of the air space for obtaining the storing-up function. 4That is why my converter.' "re-establishes so in'stantaneousl its storing-up eiect, whereas the' wel known quenching-gaps have a comparativelv large air-space between their electrodes so that the de-ionizing of these spaces requires'.

a. much longer time, in consequence whereof, in order to prevent an arc from. being maintained al condenserot great capacityzmust be provided' for keeping the 'voltage olf for' that time. -My high-frequency current-con-A verter therefore increases eilectively the output of the 'source of current, whereas with all other known gaps the current on the It is an advantage-of the new current converter that it regulates thewliole ignition energy andftherebv Quses up only as little plus potentialas a standard spark gap -of about.

0.2'to 0.4 millimeters length at usual air pressure." l

I .have now described, i.e either shunting the plug by ay high-frequency choker or-conver'ting theenergy into a series, of'J high-n v 'freq'uency impulses following one another nal combustion enginescomprising an autoiis I finally state that, besides the --two ways' iso,

matically and periodically 'yarying resistance in the' ignition circuit between the high nal combustion engines comprisi linity durin tension coil and the spark plug; said resistance varying' automatically within Wide limits, 'so that the -resistanceof thehigh-ten sioncircuit is varied several times between the limits of approximately zero and ing each magnetic impulse of the ignition apparatus. 2. A current intcrruptei' for the high tension circuit ot' an ignition circuit for intera pluralityof gaps interposed in the ignition circuit` between a high tension coil and a spark plug to create large resista-nce variations of the ignition circuit, the increase of resistance 'with decreasing current occurring in said gaps taking place so rapidly that a series of current interruptions take place at each magnetic impulse o iatus.

3. A current interrupter for the-liigh ten# sion circuit of an ignition circuit for internal combustion engines comprising 'a plurality ofA electrodes forming. a plurality of the ignition appagaps interposed in the ignition circuitbetween la high tension coil andadspak lplug to create large resistance variations of the 'ignition circuit; the increase of resistance.

with decreasing currenttaking place so rapl idly 'that a series of current interruptions ignition ap aratus, the electrodes consisting Y. of a "material which when oxidized by the r vignition. circuit, the increase' of resistance with decreasing current taking place so rap-l idly that a series ocurrent interruptions take 4place at each'magneticV impulse of the passage ofthe spark' current form an oxide which is a noir-conductor of electricity and- 5. A current interrupter for the' high tensionA circuit of an ignition circuit for an infV ternal combustion engine comprising a casing'of insulating material open -to the atmos' phere; and a plurality of electrodes in the casing'forming a plurality of gaps for creating large resistance Variations in the circuit.

causing a series of current interruptions at cach magnetic impulse of the ignition appa;

ratus.

6'. A current interrupter for the high tension circuit of an ignition circuit'for an in-A ternal combustion engine comprising av casing lotinsulating material having a vent therein forming communication with the4 atmosphere; and a plurality of electrodes in the casing forming a plurality of gaps for creating large resistance variations in the circuit causing a series of current interruptions at each magnetic impulse of the ignif tion apparatus.

7. A current interrupter for the high tension circuit of an ignition circuit for internal combustion engines comprising a tube of insulatingmaterial open tothe atmosphere' a plurality of aluminium electrodes' in sai tube to form narrow gaps in order to create a series of strong current impulses of ino-l Inentary intensity 'at the sparlr plug; and means in the tube: and cooperating with the end electrodes for securing a contact with a lead-in lwire atone end of the interrupter and for securing contact with the spark plug at the other end. a

8. "A current interrupter for the high ten sion circuit of an ignition circuitof ,an internalcombustion engine comprising a cas: ing-oil? insulating material open to the atmosphere; and a plurality of aluminium electrodes Iin the ,casing forming a pluralityo lgaps for creating large resistance variations in the circuit causing a series of current interruptions'at each magnetic impulse of the ignition apparatus.v i In testimony whereoil allix .my signature.

iieBEnf'r-voa LEPEL.' 

